Cheapest priced copy (The List): $8.99 at Card Kingdom, near mint, their price list as of .
Cavalier of Night 
Creature — Elemental Knight · 4/5 · Mythic · Core Set 2020 Promos · #94p
Lifelink
When this creature enters, you may sacrifice another creature. When you do, destroy target creature an opponent controls.
When this creature dies, return target creature card with mana value 3 or less from your graveyard to the battlefield.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $8.99 to $27.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Core Set 2020 | 94 | Mythic | $9.49 | $27.99 |
| The List | M20-94 | Mythic | $8.99 | — |
| Core Set 2020 Promos | 94p | Mythic | $21.99 | $24.99 |
| Core Set 2020 Promos | 94s | Mythic | — | $20.99 |
4 rulings from Wizards of the Coast
- 12 July 2019Cavalier of Night’s enters-the-battlefield ability goes on the stack without a target. While that ability is resolving, you may sacrifice another creature. When you do, the reflexive triggered ability triggers and you pick a target creature to be destroyed. This is different from effects that say “If you do . . .” in that players may take actions after you’ve sacrificed the creature but before the target creature is destroyed.
- 12 July 2019If a card in a graveyard has {X} in its mana cost, X is considered to be 0.
- 12 July 2019If a creature card with mana value 3 or less becomes a copy of Cavalier of Night, its last ability can target itself when it dies.
- 12 July 2019While resolving Cavalier of Night’s enters-the-battlefield ability, you can’t sacrifice more than one creature.